The Blackridge Recurrence

Fifty years ago, a train entered the Blackridge Tunnel and never came out the other side. The line was sealed, the case was buried, and the town of Blackridge learned to stop asking questions. When Ethan Blackwell, Mara Whitlock, and Daniel Cross uncover an old recording hidden in the tunnel's abandoned signal house, they find something that shouldn't exist: proof that the missing train is scheduled to reappear in exactly seven days.
As the three of them race to understand what happened five decades ago, they begin to suspect that the tunnel never lost the train at all - it simply hasn't given it back yet. With each day that passes, the boundary between what vanished and what is returning grows thinner, and Ethan, Mara, and Daniel realize that whatever comes out of Blackridge Tunnel may not be the same thing that went in.